Orthodontic arch wire edgewise brackets



2 Sheets-Sheet 1 A. C. BRADER ORTHODONTIC ARCH WIRE EDGEWISE BRACKETS June 27, 1967 Filed June 16, 1964 Fig.

INVENTOR.

A //en 6. Brader (I I mg:

By QM J I [gar Z. III.

Fig. 2

June 27, 167 A. c. BRADER ORTHODONTIC ARCH WIRE EDGEWISE BRACKETS 2 Sheets-Sheet 2 Filed June 16, 1964 Allen 6. Brader INVENTOR.

United States Patent 3,327,393 ORTHODONTIC ARCH WIRE EDGEWISE BRACKETS Allen C. Brader, 1350 Hamilton St, Allentown, Pa. 18103 Filed June 16, 1964, Ser. No. 375,555 19 Claims. (Cl. 32-14) This invention comprises novel and useful orthodontic arch wire edgewise brackets and more particularly pertains to an orthodontic appliance adapted to re-position teeth within the mouth.

It is well known in orthodontic practice to apply an arch wire carried by brackets and bearing against the sides of teeth in order by applying pressure thereto to move the teeth into a desired re-positioning in the mouth of the patient. The present invention relates to an improved bracket adapted to facilitate and render more effective the use of orthodontic arch wire for this purpose.

It is an important object of this invention to provide an orthodontic arch wire bracket which will enable the obtaining of a greater leverage and resilience in the gripping action of the arch wire.

A further object of the invention is to provide a bracket specifically adapted for systems which use edgewise brackets to support the arch wires.

A further object of the invention is to provide a bracket in accordance with the foregoing objects which will enable employing conventional technique of ligature tie wires if desired.

Still another object of the invention is to provide an orthodontic bracket for arch wires having a single lip rendering the entrance of the arch wire into the bracket slot easier than its withdrawal therefrom.

A further object of the invention is to provide a simplified construction of arch wire edgewise brackets and wherein the entrance slot of the bracket may be readily enlarged when desired to facilitate the removal of an arch wire therefrom.

These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being bad to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout, and in which:

FIGURE 1 is a perspective view showing in elevation the manner in which a first form of arch wire bracket is applied to the side of a tooth for receiving an arch wire therein, parts being broken away;

FIGURE 2 is a detail in vertical transverse section taken upon an enlarged scale substantially upon the plane indicated by the section line 2-2 of FIGURE 1;

FIGURE 3 is a view similar to FIGURE 2 but showing a second form of bracket which may be employed with the invention;

FIGURE 4 is a view similar to FIGURE 2 but of a third form of bracket in accordance with the invention;

FIGURE 5 is a view partly in elevation and partly in section taken substantially upon the plane indicated by the broken section line 5--5 of FIGURE 4;

FIGURE 6 is a persepective view of a fourth modification of an arch wire bracket;

FIGURE 7 is a view taken substantially upon the plane indicated by the section line 7-7 of FIGURE 6 Patented June 27, 1967 ice and showing an arch wire mounted in the bracket of FIGURE 6;

FIGURE 8 is an end elevational view of a fifth form of bracket;

FIGURE 9 is a view partly in elevation and partly in section taken substantially upon the plane indicated by the broken section line 9-9 of FIGURE 8;

FIGURE 10 is an end elevational view of a sixth form of bracket in accordance with the invention;

FIGURE 11 is an elevational view of the bracket of FIGURE 10;

. FIGURE 12 is a view in end elevation of a seventh form of bracket and showing an arch wire, in section therein; and

FIGURE 13 is a view partly in elevation and partly in section taken substantially upon the plane indicated by the section line 13-13 of FIGURE 12.

In the drawings accompanying this application are shown preferred embodiments of an arch wire supporting bracket in accordance with this invention, the brackets being preferably of the edgewise type. Each of the brackets includes as an integral construction a base by which the bracket is mounted upon the side of a tooth, a socket in the base having a chamber receiving the arch wire therein with means resiliently retaining the arch wire in the socket. Various arrangements of the base, the socket construction and the resilient means of the device are shown in the various embodiments. Further, although only the embodiment of FIGURES 1 and .2 discloses a bracket containing plural socket and resilient retaining units thereon, it will be appreciated that each of the other forms of the invention may likewise be formed into a plural unit device.

FIGURE 1 illustrates a conventional manner of apply? ing an arch wire to a tooth structure. Portions of teeth 10, 12 and 14 are illustrated with a conventional type of arch wire 16 being shown therein whereby it is desired to re-position the tooth It) with respect to the adjacent teeth 12 and 14. Thus there is shown a band 18 which encircles the tooth 10 and mounted upon this band either fixedly as by soldering or the like or merely by mechanically pressing thereagainst is the base 20 of an edgewise arch wire bracket indicated generally by the numeral 22. In the embodiment illustrated in FIGURES l and 2, it will be noted that the band 18 has the base 20 fixedly secured thereto and bonded thereto as by welding, brazing or the like. The base is of a flat plate-like character of a generally rectangular configuration and is provided with one or more arch wire retaining socket units each indicated by the numeral 24. As previously explained, each of the other embodiments of the invention may likewise be formed in a plurality of units to form an edgewise arch wire bracket.

With continuing reference to FIGURES 1 and 2 it will be observed that the base has mounted thereon a socket indicated generally by the numeral 26. Conveniently, this socket may consist of a U-shaped member having a pair of side walls each indicated by the numeral 28 and which are joined as by a web portion 30, the latter being fixedly secured to the base 20 in any suitable manner. Thus, the side walls 28 disposed in a generally parallel relation extend normally or perpendicularly to the base 20 and have an entrance 32 between their ends which are remote from the base.

Resilient means indicated generally by the numeral are provided for yieldingly retaining the arch wire in the base chamber. Preferably the resilient means include a pair of arms 42 which extend from the opposite side edges of the base and are preferably integral therewith, these arms being of resilient material. As shown in FIGURE 2 in particular, these arms are outwardly convergent from the base so that they have end portions 44 which extend outwardly beyond and overlie the chamber 46 in the socket 26 which receives the arch Wire 16 therein. The portions 44 of the resilient arms 42 are spaced from each other to thus provide an opening 48 which is disposed in alignment with the entrance 32 of the chamber 46. From the portions 44, the resilient arms have oppositely projecting flanges or portions 50 whose ends are curved downwardly and folded back upon themselves as at 52.

It is to be particularly noted that the portions 44 have rounded surfaces as at 54 which provide inclined surfaces of different inclinations. The arrangement is such that the resilient arms provide a lesser yielding resistance to the passage of the arch wire through the opening 48 and entrance 32 into the chamber 46 than the resistance which they present to removal of the arch wire from the chamber through the entrance and through the opening. Thus, the bracket tends to retain the arch wire in place thereby obviating the necessity of the con-' ventional ligature tie wires with which arch Wires are customarily secured to the arch wire brackets. However, the wings formed by the arms 42 and the portions 50 thereof enable ligature ties to be employed to secure the arch wires in place in accordance With conventional practice if desired.

FIGURE 3 is directed to a modified construction or bracket unit indicated generally by the numeral 60. In this form there is shownthe base 62 which is adapted to bear against the side of a tooth 10 or the band 18 thereabout. The base includes a socket having an arch wire receiving chamber 64 therein for the arch wire 66. This chamber consists of a pair of generally parallel side walls 68 as in the preceding form which provide an entrance 70 at their ends which are remote from the base. Secured to the outer ends of the side walls 68 are downturned portions 72 which extend downwardly along the side walls towards the base and from thence project outwardly therefrom as at 78 and then have outwardly converging arms 80 whose upper ends 82 overlie the entrance 70 and define an opening 84 extending beyond and aligned with the chamber and the entrance. From the ends 82, the arms have laterally directed portions as at 86. It will be observed that the ends 82 have an inclined outer surface 88 together with an inclined inner surface 90 which merge in a knife shaped edge as at 92. The ratio is such that less resistance is required to force the arch wire 66 through the guiding action of the inlet surface 88 past the knife edge 84 and into the chamber through the entrance 7 6 than would be required to remove the arch wire therefrom. The operation of this form of the invention is therefore substantially identical to that of the preceding form.

Referring next to the embodiment of FIGURES 4 and 5, it will be observed that the bracket indicated generally by the numeral is of a one-piece construction comprising a base member 102. The latter has a fiat central portion 104 together with curving looped extremities 106. These extremities project back towards the mid-portion of the base and are provided with upwardly projecting side walls 108 which are substantially parallel to each other and thus define an arch wire receiving chamber 110 therebetween with an arch wire 112 being shown received therein. At their outer extremities, the side walls 108 have inwardly projecting ribs as at 114 which define therebetween an opening 116 projecting inwardly of and being disposed above the chamber 110. From the ends 114, there project laterally extending portions 118 which 4 comprise wings. As in the other forms, the opening 116 has inner and outer inclined surfaces of different inclina tions which will as in all the other forms of the invention, facilitate the entrance of an arch wire into the chamber but resist its withdrawal therefrom with a greater resilient force.

Reference is next made to a still further form of the invention shown in FIGURES 6 and 7 and in which the bracket is indicated generally by the numeral In this form, the base 132 consists of a pair of oppositely extending loops 134 which are disposed in side by side relation fixedly joined to each other. Each of the loops 134 has a top portion 136 which extends backwardly over and beyond the central portion of the loop as shown in FIGURE 7 and from thence has an upwardly directed side wall 138. The two side walls define an arch wire receiving chamber 140 therebetween in which is received the arch wire 142. At their upper ends, the side walls 138 are provided with inwardly projecting ribs 144 which define therebetween an opening 146 which is in registration with the entrance of the chamber. From the portions 138, there are provided laterally projecting wings 148, As shown in FIGURES 6 and 7, each of the side Walls is provided with a notched or cutaway portion 150 to receive the top portion 136 of the loop of the other base portion. Thus, by manually depressing the finger grip elements 148 of the wings, the opening and entrance may be widened against the resiliency of the material of the bracket to thus permit the arch wire 142 to be withdrawn therefrom.

Referring next to the embodiment of FIGURES 8 and 9 it will be observed that the bracket unit is designated generally by the numeral 160. In this form it will be observed that the flat plate-like base 162 has at its midportion a pair of upstanding side walls 164 having an entrance 166 at their outer ends. The side walls thus define a chamber 168 in which is received an arch wire as in the preceding fonns. At their upper ends, the side walls are provided with the inwardly projecting ribs 170 which as in the other forms have inclined surfaces at their inner and outer sides of different inclinations to impose a greater resistance to movement of the arch wire out of the chamber than is required for the passage of the arch Wire into the chamber. At their outer ends, the side walls are likewise provided with oppositely outwardly directed flanges 172 which constitute finger grip means by which the entrance may be spread or enlarged. This will enable the arch wire to be satisfactorily withdrawn from the chamber when desired.

The resilient means in this form of the invention include integral arms as at 174 which are extended from the opposite sides of the baseand then are outwardly convergent to provide the opening 174 therebetween. These arms resiliently bear against the side walls 164 and urge them towards each other and thus supply all or a part of the resilience necessary for the side walls to yieldingly retain the arch wire in the chamber thereof.

A somewhat similar construction is shown in FIGURES 10 and ll wherein the numeral designates this modification of the arch wire bracket. The flat plate-like base is indicated by the numeral 182 therein and from the midportion of this base there arise the side walls 184 having upwardly convergent end portions 186 which thus define an entrance 188 therein to the arch wire receiving chamber 198. As in the preceding form, resilient arms 192 project from the opposite sides of the base and are provided with outwardly convergent portions 194 having ends 196 which bear against the side walls 184 and yieldingly urge them towards each other to supply the necessary resilience thereto. The arms 194 are provided with curving terminal portions 198 providing finger grips whereby resilient pressure may be released from the side walls 184.

The operation of this form of the invention is identical with that previously described except that the finger grip elements 198 are now carried by the spring arms 194 rather than by the side walls as in the preceding form.

A still further modified construction is shown in 'FIG- URES 12 and 13. Here, the bracket indicated generally by the numeral 260 is shown as including a base 202 resting against the tooth band 204. From the mid-portion of the base there arises a U-shaped socket 206 having the side walls 208 joined by a central web portion 210. There is thus provided an arch wire receiving chamber 212 with the arch wire 214 being shown therein. The outer ends of the side walls thus provide an entrance 216 for passage of the arch wire into and out of the chamber.

Extending from opposite sides of the base are the inwardly extending portions 218 which at their inner ends are provided with upstanding resilient arms 220 disposed in parallel relation to the side walls 206. At their upper ends these arms are provided with inwardly projecting ribs 222 Which define therebetween an opening 224 for passage of the arch wire therethrough. As in the other forms, the ribs 222 are provided with inner and outer surfaces of different inclinations which will facilitate passage of the arch wire into the chamber but will resist removal of the arch wire therefrom with a greater resilient resistance. The finger grip flanges 226 are provided enabling the resilient means to be spread apart so that the ribs 222 will enable withdrawal of the arch wire therefrom.

As previously set forth, each of the embodiments shown can be used as a single unit or as a plurality of units upon a common base as in FIGURE 1. Further, although in each of the embodiments the use of a ligature tie wire is not necessary in order to effect secure retention of the arch wire in the arch wire chamber of the bracket, the construction is such that the Wing arrangement will permit ligatures to be employed in accordance with prior conventional practice if desired.

Further, in each of the embodiments the inlet to the chamber consists of surfaces of two different inclinations such that a lesser pressure is required to force the arch wire through the inlet and into the chamber of the socket than is required to remove the arch wire therefrom.

However, not only is the gripping action of the resilient flanges enhanced by the difierences in the inclinations of the interior and exterior surfaces of the lip at the socket entrance, but the relative longitudinally offset relation of the laterally opposed, knife edged entrance lips contributes materially to an increased gripping action of the bracket upon the arch wire. This structural dis tinction is shown best in FIGURES 4, 8 and 12 wherein it will be noted that the inner surfaces or shoulders of the ribs, jaws or lips at the socket entrance are so spaced that one will be engaged by the arch wire before engagement of the other as the arch wire is being withdrawn. The first engaged lip surface of any of the several forms of brackets may be fiat, as illustrated in FIGURE 12. The purpose is to require partial resilient yielding of both of the lips or jaws so that the total yielding is divided between the two lips as the arch wire is moved into the socket thereby facilitating the entrance; but upon withdrawal to require total yielding to occur at the one lip with which the arch wire makes initial contact. The small yielding distances divided between two resilient arms offers less resistance to insertion of the arch wire into the socket than is presented by the total yielding distance required for a single lip upon withdrawal of the arch wire from the socket.

The arch wire may be of various conventional crosssectional shapes, being trapezoidal, as shown in FIG- URES 2 and 7 or being rectangular as shown in the other figures of the drawings, with the sockets being correspondingly shaped to cooperate therewith. The trapezoidal arch wire configuration will further augment the differ ences in the resistance of the lip surfaces to the insertion and the removal of the arch wires.

In one practice which is conventional in the dental profession, the ends of the arch wire are received in forwardly opening sockets provided by tubes fixedly secured to the sides of rear or molar teeth. This procedure can be advantageously replaced by the brackets of this invention, by merely omitting therefrom the laterally projecting wings such as the wings 50 of FIGURE 2, 86 of FIGURE 3, 118 of FIGURE 4, etc. This will produce a more compact structure increasing accessibility of the cheek side of the appliance for the introduction of the arch wire into the rearward or inner brackets of the appliance in contrast with prior practice which necessitates the more or less awkward and difficult insertion of the arch wire ends from the front of the mouth into the small tube openings of the brackets at the back of the mouth.

Throughout the foregoing specification, reference has been made to finger-grip means or finger-grips. It will be appreciated that the minute size of the portions will be such as to frequently preclude manipulation by human fingers. The terms used are therefore to be construed as covering manipulation of the associated bracket structure both by human fingers or by tools.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention as claimed.

What is claimed as new is as follows:

1. An orthodontic arch wire bracket comprising a base adapted for mounting upon the side of a tooth, a pair of walls rising from said base in spaced relation and having outer ends and forming an arch wire receiving chamber having an entrance between the outer ends of said walls, resilient means rising from the base and surrounding said walls and having coacting portions projecting across a portion of the entrance and overlying the chamber and causing at least a partial blocking of said entrance and imposing a greater resistance to movement of an arch wire out of said chamber than to movement of an arch wire into said chamber and said resilient means having portions outwardly projecting in opposite directions from the chamber to constitute gripping means for moving said resilient means out of blocking coaction at the entrance of the chamber.

2. An orthodontic arc wire bracket comprising a base adapted to be supported from the side surface of a tooth, a socket on said base projecting laterally therefrom and having a chamber for receiving an arch wire and having an entrance for passage of an arch wire therethrough into and out of said chamber, said socket including side walls having inner surfaces in spaced side-by-side relation disposed generally perpendicular to said base, and resilient means carried by the base and associated with one of the side walls and coacting resilient means carried by the base and associated with the other of the side walls, said resilient means adapted to cooperate to cause at least a partial blocking of the entrance and imposing a greater resistance to movement of an arch wire out of said chamber than to movement of an arch wire into said chamber.

3. An orthodontic arch wire bracket comprising a base adapted for mounting upon the side of a tooth, a pair of inner walls rising from said base and having outer ends and forming an arch wire receiving chamber having an entrance between the outer ends of said inner walls, said walls having inner surfaces disposed generally parallel with respect to each other and generally perpendicular to said base, a pair of resilient outer walls rising from the opposite sides of said base and surrounding said inner walls, said outer walls extending along the length of said inner walls in parallelism thereto and having outer ends and having at such outer ends a portion thereof projecting across a portion of said opening towards each other and overlying said chamber and entrance, said outer walls also including outwardly projecting flanges at said projecting portions.

4. The combination of claim 2 wherein said resilient means comprises wings secured to said base, said Wings having arms converging outwardly of said base and with their outer ends being spaced to provide an opening therebetween alined with said entrance, said arms outer ends having back-turned portions extending laterally from opposite sides of said opening and overlying said base.

5. The combination of claim 2 wherein said resilient means comprises wings secured to said base and including arms converging outwardly of said base and overlying at least a portion of said socket and having spaced outer ends providing an opening therebetween alined with said entrance, said arms outer ends having back-turned portions projecting laterally from opposite sides of said opening.

6. The combination of claim 2 wherein said base has its opposite end portions folded back upon themselves, side portions on said folded back end portions disposed in parallel relation and defining therebetween said socket and chamber, the outer ends of said side portions having inwardly projecting lips defining with said side portions said resilient means and having outturned portions overlying said base and said folded back opposite end portions.

7. An orthodontic arc wire bracket comprising a base adapted for mounting upon the side of a tooth, a pair of generally parallel inner walls rising from said base and forming an arch wire receiving chamber having an entrance between the outer ends of said inner walls, a pair of resilient outer walls rising from the opposite sides of said base and surrounding said inner walls, said outer walls being outwardly converged from said base, and having an opening between the convergent ends thereof overlying and alined with said entrance and being of less width than the latter, the extremities of said convergent ends being turned back upon said outer walls and projecting oppositely and laterally from said opening.

8. An orthodontic arch wire bracket comprising a base adapted for mounting upon the side of a tooth, a pair of generally parallel inner walls rising from said base and forming an arch wire receiving chamber having an entrance between the outer ends of said inner walls, a pair of resilient outer walls rising from the opposite sides of said base and surrounding said inner walls, said outer walls extending along the length of said inner walls in parallelism thereto and at their outer ends having retaining ribs projecting across said opening towards each other and overlying said chamber and entrance, outwardly projecting flanges on said outer walls at said ribs.

9. An orthodontic arch wire bracket comprising a base adapted for mounting upon the side of a tooth, a pair of generally parallel inner walls rising from said base and forming an arch wire receiving chamber having an entrance between the outer ends of said inner walls, a pair of resilient arms each joined to the upper end of one of said inner walls and extending downwardly along the outer sides of the latter to said base and from thence projecting longitudinally from opposite ends of said base and having upwardly convergent wings whose ends are disposed above said chamber entrance and overlie the latter.

10. The combination of claim 9- wherein said ends of said wings form an opening with a V-shaped edge with inclined side surfaces converging towards said V-shaped edge, the side surfaces on the outside of said wings having a steeper inclination than that on the inner sides.

11. An orthodontic arch wire bracket composed of a base adapted for mounting upon the side of a tooth together with a-socket on said base having an arch wire receiving chamber with an entrance and resilient retaining means at least partially blocking said entrance, said base consisting of a pair of vertically disposed loops in side by side engagement in opposite directions, the top portion of each loop extending from an end of said base inwardly beyond the base midportion and having an upwardly projecting wall with an outwardly projecting flange at the upper end of each wall, said walls defining an arch wire receiving chamber having an entrance between the upper ends of said walls, inwardly projecting ribs on the inner surfaces of said walls projecting across said entrance and having sloping guide surfaces yieldingly resisting passage of said arch wire through said entrance.

12. An orthodontic arch wire bracket composed of a base adapted for mounting upon the side of a tooth together with a socket on said base having an arch wire receiving chamber with an entrance and resilient retaining means at least partially blocking said entrance, a pair of generally parallel side walls rising from the mid-portion of said base and defining an arch wire receiving chamber therebetween with an entrance formed by the upper ends of said side walls, a pair of spring arms rising each from one side of said base, each spring arm having an upper portion inturned towards and resiliently bearing against a side Wall and yieldingly resisting opening of said entrance and passage of an arch wire therethrough, inwardly projecting lips 0n the inner surfaces of said side walls at said entrance.

13. The combination of claim 11 including outwardly projecting flanges comprising handles on the upper ends of said side walls.

14. The combination of claim 11 including outwardly projecting flanges comprising handles on the upper ends of said spring arms.

15. An orthodontic appliance comprising in combination an arch Wire and a band mounted upon a tooth to be repositioned in a mouth, a bracket for mounting upon said band and receiving said arch wire in detachable engagement in said bracket, said bracket comprising a base supported from the side surface of the band, a socket on said base projecting laterally therefrom and having a chamber receiving said arch wire and having an entrance for passage of said arch wire therethrough int-o and out of said chamber, said socket including side walls having inner surfaces in spaced side-by-side relation disposed generally parallel to each other and generally perpendicular to said base and resilient means carried by the base and associated with one of the side walls and coacting resilient means carried by the base and associated with the other of the side walls, said resilient means adapted to cooperate to cause at least a partial blocking of the entrance and imposing a greater resistance to movement of an arch wire out of said chamber than movement of an arch wire into said chamber.

16. The combination of claim 15 wherein said base has a pair of substantially parallel resilient side walls rising perpendicularly from its mid-portion and defining an arch wire receiving chamber, the upper ends of said side walls having inwardly projecting ribs in said entrance to said chamber, flanges on the upper ends of said side walls extending oppositely and constituting means for spreading said side walls and opening said entrance.

1.7. The combination of claim 16 wherein said base and side walls are connected by loop portions.

18. The combination of claim 2 wherein said resilient means comprises a pair of laterally opposed yieldable lips at said chamber entrance, the inclination of the exterior surfaces of said lips being less than the inclination of the lips interior surfaces at said entrance thereby producing a differential resistance to passage of an arch wire into and out of said chamber.

19. The combination of claim 2 wherein said resilient means comprises a pair of laterally opposed yieldable lips at said chamber entrance, the interior surfaces of said lips being spaced longitudinally of each other from the inner end of said chamber whereby to cause an arch wire to initially engage solely the innermost of said lip interior surfaces when moving the arch. wire outwardly from said base and out of said chamber.

(References on following page) References Cited UNITED STATES PATENTS FOREIGN PATENTS 1,061,053 7/1959 Germany. Kellner 24-259 120,009 10/1918 Great Britain. Young 3214 5 C0nad ROBERT E. MORGAN, Acting Primary Examiner. $512,162;:Ijjjiiiifiiii RICHARD A GAUDET, Wallshein 32-14 J. W. HINEY, JR., Assistant Examiner. 

1. AN ORTHODONTIC ARCH WIRE BRACKET COMPRISING A BASE ADAPTED FOR MOUNTING UPON THE SIDE OF A TOOTH, A PAIR OF WALLS RISING FROM SAID BASE IN SPACED RELATION AND HAVING OUTER ENDS AND FORMING AN ARCH WIRE RECEIVING CHAMBER HAVING AND ENTRANCE BETWEEN THE OUTER ENDS OF SAID WALLS, RESILIENT MEANS RISING FROM THE BASE AND SURROUNDING SAID WALLS AND HAVING COACTING PORTIONS PROJECTING ACROSS A PORTION OF THE ENTRANCE AND OVERLYING THE CHAMBER AND CAUSING AT LEAST A PARTIAL BLOCKING OF SAID ENTRANCE AND IMPOSING A GREATER RESISTANCE TO MOVEMENT OF AN ARCH WIRE OUT OF SAID CHAMBER THAN TO MOVEMENT OF AN ARCH WIRE INTO SAID CHAMBER AND SAID RESILIENT MEANS HAVING PORTIONS OUTWARDLY PROJECTING IN OPPOSITE DIRECTIONS FROM THE CHAMBER TO CONSTITUTING GRIPPING MEANS FOR MOVING SAID RESILIENT MEANS OUT OF BLOCKING COACTION AT THE ENTRANCE OF THE CHAMBER. 